The present invention relates generally to photographic exposure equipment, and more particularly, to a photolithography system and method, such as can be used in the manufacture of semiconductor integrated circuit devices.
In conventional photolithography systems, the photographic equipment requires a mask for printing a pattern onto a photo resist coated subject. The subject may include, for example, a semiconductor substrate for manufacture of integrated circuits, metal substrate for etched lead frame manufacture, conductive plate for printed circuit board manufacture, or the like. A patterned mask or photomask may include, for example, a plurality of lines, structures, or images. During a photolithographic exposure, the photo resist coated subject must be aligned to the mask very accurately using some form of mechanical control and sophisticated alignment mechanism.
With conventional photolithography, the patterned masks are typically very expensive. In addition, the photomasks are characterized as requiring a very long mask purchase lead time. The long mask purchase lead time is not very helpful when a short product development cycle is desired. Further, if a particular mask design is found to require a design change in the pattern, no matter how small of a then mask modification cost and a respective lead time to implement the required change can cause serious problems in the manufacture of the desired product.
A mask is typically made at a mask printing manufacturer or mask shop, for example, with the use of a very sophisticated electron beam direct writing system or photography system to print a desired design pattern onto a transparent substrate material, such as a quartz glass plate. In addition, highly sophisticated computer systems may also be necessary. Masks are, in general, delicate items that must be continually handled. For one, a photolithography system must continually change between masks for different products, or for different portions or layers on a specific product. Also, masks must be stored and handled for routine maintenance operations on the photolithography system. As a result, using masks can be add significant cost to the overall photolithography process.
Referring briefly now to FIG. 1, a conventional photolithography system 10 is illustrated. The photolithography system 10 includes a light source 12, a first lenses system 14, a printed mask 16, a mask alignment system 18, a second lenses system 20, a subject 22, and a subject alignment system 24. The subject 22 may include a photo resist coating 26 disposed thereon. During photolithography, light 28 emanates from the light source 12, through the first lenses system 14, the printed mask 16, the second lenses system 20, and onto the subject 22. In this manner, the pattern of the mask 16 is projected onto the resist coating 26 of the subject 22.
The mask 16 must be aligned to the subject 22. At a minimum, there are five different alignments. These alignments may be accomplished by one or both of the mask alignment system 18 and the subject alignment system 24. For the sake of example, the subject 22 may be a wafer with one or more alignment marks that must align to marks on the mask. First of all, the wafer 22 must be horizontally aligned (in both an x-direction and a y-direction) to center the alignment marks with on the wafer and mask. The wafer 22 must also be rotationally aligned (rotated) and must be vertically aligned (in a z-direction, e.g., placed in focus). The wafer 22 and/or the mask 16 must also be tilt aligned so that all of the edges of the wafer are in focus.
As the demand for integrated circuits with more logic and/or higher speed (e.g., with increased memory and processing capability) rises, the individual feature sizes (e.g., line width) on the integrated circuits must be reduced. To achieve this reduced line width, the photolithography equipment used for imaging these patterns must have higher and higher resolution. Simultaneously, the larger physical size of the integrated circuits demands that the higher resolution be achieved over a larger image field.
The photolithography system 10 achieves relatively high resolution by using the first and second lenses system 14, 20, so that the pattern on the mask 16 can be reduced by a factor of 5xc3x97 to 10xc3x97 on the subject 22. Since such a lense reduction system is capable of high resolution only over a limited image field, the exposure region is confined to specific step xe2x80x9csites.xe2x80x9d That is, the entire subject 22 is processed by exposing a site, stepping to the next site, and repeating the process. In these prior art systems, known as step and repeat systems, the limiting performance capability is determined by the reduction projection lens assembly, which typically consists of a large number of individual lens elements. As the resolution requirements increase, the design complexity of the corresponding lens assembly increases. Furthermore, a complicated lens system is required to compensate for the effects of the undesired diffracted light.
Therefore, it is desired to eliminate or reduce the problems in the art associated with conventional masks.
It is also desired to provide a lithographic system and method with increased resolution.
It is further desired to provide an improved photolithography alignment system, such improvement being in alignment accuracy, alignment speed, automation, and/or other requirements of alignment.
It is still further desired to provide an improved photolithography system where light diffraction problems associated with conventional photolithographic masks are reduced or eliminated.
A technical advance is achieved by a novel system and method for photolithography which provides a moving digital image onto specific sites on a subject. In one embodiment, the method projects a pixel-mask pattern onto a subject such as a wafer. The method provides a sub-pattern to a pixel panel pattern generator such as a deformable mirror device or a liquid crystal display. The pixel panel provides a plurality of pixel elements corresponding to the sub-pattern that may be projected onto the subject.
Each of the plurality of pixel elements is then simultaneously focused to discrete, non-contiguous portions of the subject. The subject and pixel elements are then moved (e.g., by vibrating one or both of the subject and pixel elements) and the sub-pattern is changed responsive to the movement and responsive to the pixel-mask pattern. As a result, light can be projected into the sub-pattern to create the plurality of pixel elements on the subject, and the pixel elements can be moved and altered, according to the pixel-mask pattern, to create a contiguous image on the subject.
In some embodiments, the method also removes diffracted light from each of the pixel elements by passing the pixel elements through a grating or shadow mask.
In some embodiments, the step of focusing simultaneously creates a plurality of coplanar focal points on the subject. This can be accomplished, for example, through a microlense array.
In some embodiments, the pixel-mask pattern is aligned with the subject prior to providing the sub-pattern to the pattern generator by adjusting the sub-pattern before it is provided.
In some embodiments, the step of changing the pixels is accomplished by sequentially providing a plurality of bit maps. Each of the bit maps is used to create the sub-patterns.
In some embodiments, the subject can be divided into a plurality of contiguous micro-sites. The pixel elements are moved relative to the subject by simultaneously scanning in a predetermined fashion throughout each of the microsites, so that the pixel-mask pattern eventually creates a contiguous image across the plurality of contiguous micro-sites.
In some embodiments, the pixel elements are moved by a vibrating mirror and the pixels are changed corresponding to the vibration of the mirror.
Therefore, an advantage of the present invention is that it eliminates or reduces the problems in the art associated with conventional masks.
Another advantage of the present invention is that it provides a lithographic system and method with increased resolution.
Yet another advantage of the present invention is that it provides an improved photolithography alignment system, such improvement being in alignment accuracy, alignment speed, automation, and/or other requirements of alignment.
Still another advantage of the present invention is that it provides an improved photolithography system where light diffraction problems associated with conventional photolithographic masks are reduced or eliminated.